1. Field of the Invention
The present invention relates to a processing machine for performing a bending operation and a bending method.
2. Description of Related Art
There is known a processing machine for performing a bending operation on a plate-like workpiece by placing the workpiece on a die and pressing a punch against the workpiece. Japanese Patent Application Laid-open No. 2006-263815 describes such a processing machine. This processing machine is configured such that a pressure cam block disposed slidably on inclined surfaces of punches located on the side opposite to a die is moved in parallel to the die for moving the punches toward the die to thereby bend a workpiece. The punches are pressed against the workpiece successively in the order from the one whose inclined surface is the closest to the starting point of the pressure cam block so that the workpiece is formed in a corrugated shape having bumps and dents.
In the processing machine described above, the punches are pressed against the workpiece successively when the pressure cam block moves from the starting point to an end point at a load depending on the pressure angle of the inclined surfaces. Accordingly, if the pressure angle is excessively large, it may occur that the plastic deformation of the workpiece is insufficient, and the workpiece slightly returns its original shape. In this case, the shape accuracy of the corner R portions and the shape accuracy of the flat portions at the crests of the bumps and the valleys of the dents of the workpiece formed in a corrugated shape may be degraded. Incidentally, if the pressure angle of the inclined surfaces of the punches is reduced for increasing the load applied from the punches to the workpiece, the size of the processing machine increases because the travel distance of the pressure cam block increases.